In this letter, we propose an FFT-based SNR estimation method for wireless OFDM systems, and analyze the impact of the proposed SNR estimation method on adaptive OFDM performance in slow Rayleigh fading channels. Numerical and simulation results show that the proposed method is effective and feasible for adaptive modulation in slow Rayleigh fading channels.

Multipath search based instantaneous root-mean-squared (RMS) delay spread (RDS) estimators mainly depend on path detection or multipath search. This paper proposes a novel method for multipath search through Minimum Descriptive Length (MDL) criterion, and hence a novel instantaneous RDS estimation method for wireless OFDM systems. compared with the conventional multipath search based instantaneous RDS estimators, the proposed estimator doesn't need any a priori information about the noise variance and the channel power delay profile (PDP) while the performance is improved. Simulation results demonstrate that the proposed estimator is also insensitive to the variance of SNR and robust against the frequency selectivity, as well as the vehicle speed.